Threading, grooving and profiling of metals by turning on a lathe are well known. The cutting tool is a throw-away insert detachably mounted in a tool holder. The tool holder is, in turn, mounted on a tool slide and carriage for precision movement radially and parallel to the axis of rotation of the metal. Exemplary of the art found is U.S. Pat. Nos. 2,598,581, 2,641,049, 2,737,705, 2,787,823, 2,846,756, 2,961,743, 2,964,833, 2,967,345, 2,976,028, 3,090,104, 3,324,529, 3,354,527, 3,377,685, 3,383,748, 3,488,822 and 3,557,416.
A primary problem is that such cutting inserts must be rigidly indexed with precision in the tool holder for precision working of the metal. The problem is particularly acute in profiling operations where complex workpiece configurations are formed. The forces exerted on the cutting insert by the machine tool are changing and varying. Moreover, the depth of the cut taken, thickness of the chips taken, the actual cutting edge of the insert used, and the direction of the chip flow across the cutting edge of the insert are changing and varying.
Particularly for profiling, the standard means utilized for indexing cutting inserts in the tool holder has been a V-shaped bottom which runs the length of the insert. The V-shaped bottom mates with an opposite V-shaped groove in the tool holder. The difficulty is that these V-shaped bottoms are expensive to make because they must be formed by precision machining and grinding. Cutting inserts are typically made from tungsten carbide by pressing and sintering a fine powder according to well-established procedures. This technique involves substantial shrinkage so that dimensions cannot be held in close tolerances; and machining and grinding of tungsten carbide requires diamond-cutting and abrading means.
It has been proposed to eliminate the V-shaped bottom by indexing the insert with a top notch, called a "whistle notch." That is, a groove extending obliquely across the top of the insert at an angle of about 45.degree. to 50.degree. to the indexing surface. The notch is engaged and the cutting insert indexed by a bridge clamp extending from the tool holder. The prime problem with these top-notch inserts is that the tool cannot be fed to the workpiece in both the forward and reverse directions. Furthermore, such top-notch inserts are of limited life because they cannot be reindexed to a new cutting edge by rotation. The insert may be given additional life by providing cutting edges at opposite ends and flipping the insert to the new cutting edge. In addition, such inserts are asymmetric in configuration which makes them complicated and expensive to form.
The present invention overcomes these difficulties and disadvantages. All portions of the cutting edges can be utilized on each insert. The inserts also provide for a universal tool holder assembly which can be used for threading and grooving as well and profiling.